Electrophysiology is a specialty within the field of cardiology for the diagnosis and treatment of electrical abnormalities of the heart. Certain types of abnormalities are caused by acyclic electrical activity within the heart due to aberrant accessory atrioventricular pathways.
These include atrial flutter, atrial fibrillation and ventricular tachycardia.
These forms of cardiac disorders can be diagnosed using an electrophysiology catheter positioned at the ventricular side of the mitral annulus. A local bipolar electrogram is recorded and signals from recording electrodes in contact with endocardial tissue which are present at different locations are electrically averaged. However, during orthodromic tachycardia and in particular during ventricular stimulation, the direction of the ventricular activation sequence can be situated parallel to the recording dipole resulting in a large amplitude ventricular signal and therefore complicating the diagnosis procedure. Moreover, the detection of retrograde atrial activation in the wake of a large ventricular complex is further complicated by short ventricular-atrial conduction delays located near the accessory pathway resulting in a problematic recording of retrograde atrial activity when using a conventional catheter tip below the mitral annulus in patients with a concealed left side accessory pathway.
Once detected, these forms of cardiac disorders can be treated by destroying the causative heart tissue through radio frequency (RF) catheter ablation. Accessory pathways are ablated using an electrophysiology catheter guided into the heart through a vein or artery which is positioned at the site of the causative accessory pathway. RF energy sufficient to destroy heart tissue is emitted from the catheter tip and the ablated tissue is replaced by scar tissue which interrupts the accessory pathway and restores the normal conduction of electrical activity within the heart.
An electrophysiology diagnosis and ablation catheter with a high-performance filter system is shown in International Patent Application WO 92/21285, filed May 24, 1991 to S. D. Edwards et al. The catheter probe has a terminal tip portion with a tip electrode carried on its distal end. A reference electrode for supplying a reference potential signal is located 3-10 mm proximally from the tip electrode in the side of the catheter shaft. An ablating electrode for providing electromagnetic energy is located adjacent but electrically insulated from both the tip and reference electrodes. The tip and reference electrodes generate and record (map) monophasic action potentials while the ablating electrode ablates endocardial tissue. Since only the ablating electrode ablates, the size and formation of ablative injury is limited by the position and orientation of this sole electrode. Moreover, the reference electrode is preferably flush or recessed from the catheter shaft and only contacts blood, not endocardial tissue, thereby limiting its ability to detect retrograde atrial potentials.
Therefore, what is needed is an electrode catheter having an ablation electrode at its tip capable of performing both cardiac mapping and ablation of heart tissue thereby resulting in a more controllable lesion size and enhanced efficacy of treatment.